Spinal implant surface configuration with a projection having a back cut

ABSTRACT

The present invention is a specialized implant having opposed surfaces for engaging each of the vertebral bodies adjacent a disc space into which the implant is implanted. The surface comprises arrayed projections having at least one forward facing facet directed at least in part toward the leading end of the implant and at least one rearward portion directed at least in part toward the opposite trailing end of the implant. Each of the forward facet and rearward portion has a length and a slope. The length of the forward facet is longer than the length of the rearward facet. The slope of the rearward facet is steeper than the slope of the forward facet. The surface projections also have opposed side facets directed generally toward the sides of the implant. The side facets are located between the forward facet and rearward facet and converge toward each other in a direction away from the base of the surface projections. The surface may also include projections having left and right forward side facets and a rearward facet. The surface further may include projections having left and right rearward side facets and a forward facet.

[0001] This application is a continuation of application Ser. No.09/457,228, filed Dec. 8, 1999, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION DESCRIPTION OF THE RELATED ART

[0002] The present invention relates to interbody spinal implants forplacement between adjacent vertebral bodies of a human spine, and morespecifically to a specialized surface for such interbody implants, forengaging the adjacent vertebral bodies. Vital to the functioning of allinterbody spinal implants is their ability to remain properly locatedwithin the spine after installation. In U.S. Pat. Nos. 5,593,409 and5,609,635, Michelson described the use of surface roughenings, such asknurling or ratcheting on the opposed upper and lower vertebral bodyengaging surfaces of interbody spinal fusion implants. Knurling has beenparticularly beneficial for increasing the grip of the implant surfaceto the adjacent vertebral bodies in a rather uniform manner without adirectional bias. Spinal implants have a propensity to move in aparticular direction, which is opposite to their path of insertion,because this is the path of least resistance. Such propensity to move isfurther increased when the opposed upper and lower vertebral bodyengaging surfaces are in angular relationship to each other, such thatthey are spaced further apart at the implant's trailing end than at theimplant's leading end. In such circumstances where it is desirable thento gain stability in resistance to a particular direction of movement ofthe interbody spinal implant, the use of a plurality of forward facingratchetings on the implant's vertebral body engaging surfaces has beenpreferable to the previously described knurling for that purpose.

[0003] The term “ratcheting” as used herein is defined as a plurality ofangular teeth or ridges or protrusions projecting from the surface of animplant to resist motion of the implant at least in one direction. Thephrase “forward facing ratchetings” as used herein is defined as aratcheting having at least one forward facing facet having a lengthgreater than a rearward facing facet and an angle from the implantsurface from which the forward facing facet arises that is less steepthan the angle of the rearward facet. On an implant surface, forwardfacing ratchetings facilitate the insertion of the implant in onedirection and after insertion, resisting movement of the implant in adirection opposite to the direction of insertion. An example of forwardfacing ratchetings of the prior art is shown in partial fragmentary viewin FIGS. 24A and 24B, generally referred to by the reference numeral 50.

[0004] Knurled surfaces of the related art provide some stability in alldirections, but lack the ability to resist a particular direction ofmotion preferentially. The above-described ratcheted surface bestresists motion in a particular direction. There exists a need for animproved interbody spinal implant surface configuration, wherein theopposed upper and lower vertebral body engaging surfaces of the implantare configured to be resistant to implant movement in all directions,and preferentially or in particularly in one direction.

SUMMARY OF THE INVENTION

[0005] The present invention relates to interbody spinal implants havinga specialized surface configuration on the opposed exterior surfacesadapted for engaging the vertebral bodies adjacent a disc space intowhich the interbody implant is to be implanted. Such an implant surfaceconfiguration has utility with a wide variety of shapes of interbodyspinal implants where enhanced skeletal fixation is desired. Such animplant surface configuration can provide for enhanced stability,increased surface area, and a surface for the delivery of fusionpromoting substances other than bone. In a preferred embodiment, theimplant surface can provide for resisting motion in all directions, andparticularly in at least one direction, such as counter to the directionof insertion of the implant.

[0006] While various embodiments of the present invention are presentedby way of example only and not limitation, common to each of them isthat the surface configuration incorporates a plurality of spatiallyintegrated surface projections having at least one forward facing facetdirected at least in part toward the leading end of the implant and atleast one rearward portion directed at least in part toward the oppositetrailing end of the implant. By way of example and not limitation, therearward portion may be a facet, a line, or an edge of the rearwardaspect of the surface projection formed where two facets come together.Each of the forward and rearward facets have a length and a slope. Thelength of the forward facet is longer than the length of the rearwardfacet. The slope of the rearward facet is steeper than the slope of theforward facet. In various embodiments, the surface projections also haveopposed side facets directed generally toward the sides of the implant.The side facets are located between the forward facet and rearward facetand may converge toward each other in a direction away from the base ofthe surface projections. The surface comprises multifaceted ratchetedprojections that are organized in geometrically disposed fields orarrays which are at a minimum located on at least a portion of theopposed vertebral body engaging surfaces of the implant. From theteachings disclosed herein, it is appreciated that the surfaceprojections can be geometrically arranged in a pattern wherein at leasta portion of the projection is aligned along a longitudinal, horizontal,diagonal, or curved line. The upper and lower surfaces of the implantcan be at least in part arcuate or planar and can converge along aportion or all of the length of the implant.

[0007] In various preferred embodiments of the present invention, therearward facets of the surface projections can be perpendicular or atangles greater or less than 90 degrees to at least one of the upper orlower surfaces of the implant from which the projections arise. Theopposed side facets of the surface projections can have at least a firstportion in a plane at an angle to the longitudinal axis of the implant.The opposed side facets can intersect each other, and can converge toform a peak at the top of each of the surface projections. The peaks canbe aligned along lines that are perpendicular, parallel, or diagonal tothe longitudinal axis of the implant. The surface projections can becleaved such as by longitudinal and/or horizontal cuts to increase thenumber of exposed sides of the projections and thus increase theavailable surface area to contact and engage the bone of the adjacentvertebral bodies and increase the number of recessed areas to containfusion promoting substances. Alternatively, the peaks of each surfaceprojection can be cleaved, truncated, or flattened at least in part.

[0008] The surface projections can include a left forward side facet anda right forward side facet directed toward the leading end and sides,respectively, of the implant. Similarly, the surface projections caninclude a left rearward side facet and a right rearward side facetdirected toward the trailing end and sides, respectively, of theimplant. The side facets of adjacent surface projections can be spacedapart to define a groove therebetween. A plurality of adjacent surfaceprojections can be spaced apart to form a plurality of grooves that canbe parallel or at an angle to the longitudinal axis of the implant,wherein the angle can be less than 90 degrees. The grooves can have ahorizontal cross section that is a V-shape, U-shape, or a box-likeshape, for example.

[0009] Sequential projections can be positioned on an implant whereineach surface projection has forward facing facets facing the samedirection, such that consecutive projections are oriented forward facingfacet to rearward facing facet. The lower most portion of the slope ofthe forward facing facet of a first surface projection in a sequence canbe coincident with the rearward facet of the next surface projection inthe sequence. Alternatively, the forward facet of a first surfaceprojection and the rearward facet of the next surface projection in asequence can be spaced apart and the space can be at least in part flat,curved, or any other surface contour suitable for the intended use. Thesurface projections can be oriented relative to one another to formfields or arrays that further can be geometrically disposed relative toone another, preferably in a pattern wherein at least a portion of theprojection is aligned along a longitudinal, horizontal, diagonal, orcurved line.

[0010] The surface configuration of the present invention can be formedby casting, machining, or any other techniques known to one of ordinaryskill in the art. The present surface configuration may readily bemachined by milling the implant surface from side to side, across theupper and lower vertebral body engaging surfaces, to form ratchetingsgenerally disposed perpendicular to the long axis of the implant andgenerally formed facing to the insertion end of the implant. Theratchetings may be cross machined with an angled cutting face to formgrooves passing through the ratchetings. For example, a milling machinehaving a cutting tool, with a V-shaped profile, can be run through theplurality of ratchetings parallel to the longitudinal axis of theimplant to form the above-described surface. In a preferred embodiment,the V-shaped cutting tool of the milling machine has opposed cuttingfaces with an angle of approximately 90 degrees to each other, whichfaces are each at a 45-degree angle to the plane of the surfaces beingmachined. Without departing from the scope of the present invention, theangle of the cutting faces can be more or less than 90 degrees, and theangle of the cutting face to the surface to be cut can be more or lessthan 45 degrees. It is appreciated that rather than the cutting elementbeing run parallel to the longitudinal axis of the implant, the cuttingelement could be run at some other angle. By way of example only and notlimitation, this angle could be at 45 degrees to the longitudinal axisof the implant and to the projections. Each surface projection couldthen be formed by a cutter crossing in two passes to form two grooves ata 90 degree angle to each other.

[0011] The surface of the present invention for engaging each of theadjacent vertebral bodies may be incorporated into various types ofspinal implants. Such spinal implants may be for the purpose ofachieving interbody spinal fusion, or for stabilizing a device to spaceapart and allow motion between the adjacent vertebral bodies. Suchspinal implants may comprise any artificial or naturally occurringmaterial appropriate for the intended purpose. Such materials wouldinclude, but are not limited to, implant quality metals, including, butnot limited to, titanium and its alloys, surgical grade plastics andplastic composites which may or may not be bioresorbable, ceramics, andcortical bone. Some examples of interbody spinal implants that maybenefit from the present teaching, include but are not limited to thefollowing patents and applications by Michelson which are incorporatedby reference herein: U.S. Pat. Nos. 5,015,247; 5,522,899; 5,593,409;5,609,635; 5,860,973; and application Ser. No. 08/480,904.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a top plan view of an interbody spinal implant having asurface configuration in accordance with the present invention.

[0013]FIG. 1A is a perspective view of an implant having arcuatesurfaces and an end cap in accordance with an embodiment of the presentinvention.

[0014]FIG. 1B is a top elevational view of an implant having a leadingend, a trailing end, and sides forming a circle in accordance with anembodiment of the present invention.

[0015]FIG. 1C is a graphical representation of a motion preservingdevice in accordance with an embodiment of the present invention.

[0016]FIG. 2 is a side elevation view of the spinal implant of FIG. 1.

[0017]FIG. 3 is a side elevation view of the interbody spinal implant ofFIG. 1 installed in an implantation site formed across the disc spacebetween two adjacent vertebral bodies of the spine shown in partialcross-section.

[0018]FIG. 4 is an enlarged fragmentary top plan view of an implantsurface of one embodiment of the present invention from a view takenalong area 4 of FIG. 1.

[0019]FIG. 5 is a fragmentary side elevation view of the implant surfaceof FIG. 4 from a view taken along area 5 of FIG. 2.

[0020]FIG. 6 is a fragmentary end elevation view of FIG. 4.

[0021]FIG. 7 is a fragmentary perspective view of the implant surface ofFIG. 4.

[0022]FIG. 8 is an enlarged fragmentary top plan view of a secondembodiment of the implant surface of the present invention from a viewtaken along area 8 of FIG. 1.

[0023]FIG. 9 is a fragmentary side elevation view of the implant surfaceof FIG. 8 from a view taken along area 9 of FIG. 2.

[0024]FIG. 10 is a fragmentary end view of the implant surface of FIG.8.

[0025]FIG. 11 is a fragmentary perspective view of the implant surfaceof FIG. 8.

[0026]FIG. 12A is an enlarged fragmentary top plan view of a thirdembodiment of the implant surface of the present invention from a viewtaken along area 12 of FIG. 1.

[0027]FIG. 12B is an enlarged fragmentary top plan view of anotherembodiment of the implant surface of the present invention from a viewtaken along area 12 of FIG. 1.

[0028]FIG. 13 is a fragmentary side elevation view of the implantsurface of FIG. 12A from a view taken along area 13 of FIG. 2.

[0029]FIG. 14 is a fragmentary end view of FIG. 12A.

[0030]FIG. 14A is an enlarged fragmentary side view of a groove having aU-shape in accordance with an embodiment of the present invention from aview taken along area 14A of FIG. 14.

[0031]FIG. 14B is an enlarged fragmentary side view of a groove having abox-shape in accordance with an embodiment of the present invention froma view taken along area 14B of FIG. 14.

[0032]FIG. 14C is a fragmentary end view of a plurality of surfaceprojections spaced apart from one another in accordance with anembodiment of the present invention.

[0033]FIG. 15 is a fragmentary perspective view of the implant surfaceof FIG. 12A.

[0034]FIG. 16 is an enlarged fragmentary top plan view of a fourthembodiment of the implant surface of the present invention from a viewtaken along area 16 of FIG. 1.

[0035]FIG. 17 is a fragmentary side elevation view of the implantsurface of FIG. 16 from a view taken along area 17 of FIG. 2.

[0036]FIG. 18 is a fragmentary end view of FIG. 16.

[0037]FIG. 19A is an enlarged fragmentary perspective view of theimplant surface of FIG. 16.

[0038]FIG. 19B is an enlarged fragmentary perspective view of avariation on the second and third surface projections of the fourthembodiment of the implant surface of the present invention with a cleavetherethrough.

[0039]FIG. 20 is an enlarged fragmentary top plan view of a fifthembodiment of the implant surface of the present invention from a viewtaken along area 20 of FIG. 1.

[0040]FIG. 21 is a fragmentary side elevation view of the implantsurface of FIG. 20 from a view taken along line 21 of FIG. 2.

[0041]FIG. 22 is a fragmentary end view of FIG. 20.

[0042]FIG. 23 is an enlarged fragmentary perspective view of the implantsurface of FIG. 20.

[0043]FIGS. 24A and 24B are perspective and side elevation views,respectively, of a prior art implant surface having forward facingratchetings.

DETAILED DESCRIPTION OF THE DRAWINGS

[0044] As shown in FIGS. 1-7, an interbody spinal implant 100 has aleading end 102, a trailing end 104, an upper surface 106, a lowersurface 108, and a side wall 110 between upper and lower surfaces 106,108. Upper and lower surfaces 106, 108 may converge from trailing end104 to leading end 102 along a longitudinal axis L of implant 100 asshown, or may diverge, be parallel, or any combination thereof. Upperand lower surfaces 106, 108 are configured to be placed against and incontact or engagement with the bone of vertebral bodies V of twoadjacent vertebrae adjacent disc D of the human spine. Upper and lowersurfaces 106,108 and side wall 110 may include large and/or smallopenings 112, 114, and 116, respectively, to permit bone growth into andthrough implant 100. Upper and lower surfaces 106,108 of implant 100 canbe generally planar as shown in the figures, or can be opposed arcuatesurfaces as shown and described in U.S. Pat. No. 5,593,409, incorporatedherein by reference, or any other configuration suitable for the desireduse.

[0045] As shown in detail in FIGS. 4-7, at least a portion of upper andlower surfaces 106, 108 of implant 100 have a surface configurationgenerally referred to by the numeral 120. In accordance with a firstembodiment of the present invention, surface configuration 120 includessurface projections 122 configured to facilitate insertion of implant100 into an implantation site while resisting expulsion of implant 100in a direction opposite to the direction of insertion. Each of surfaceprojections 122 has an angled forward facet 124 directed at least inpart toward leading end 102 of implant 100 and a rearward facet 126directed at least in part toward trailing end 104 of implant 100.Forward facet 124 has a length greater than the length of rearward facet126. Rearward facet 126 has a slope that is steeper than the slope offorward facet 124. In this embodiment, the base of rearward facet 126forms an angle of approximately 90 degrees with respect to upper and/orlower surfaces 106, 108 of implant 100. It is appreciated that the angleof the base of rearward facet 126 with respect to upper and/or lowersurfaces 106, 108 of implant 100 may be perpendicular to, greater thanperpendicular to, or less than perpendicular to the base of the surfacewhere the facet arises. Forward facet 124 forms an angle in the range ofapproximately 10 to 60 degrees, with 25-45 degrees being preferred, withrespect to upper and/or lower surfaces 106, 108. Each one of surfaceprojections 122 also has a left side facet 132 and a right side facet134 directed toward the sides of implant 100.

[0046] In this embodiment of surface configuration 120, a plurality ofsurface projections 122 are spaced apart laterally (side to side) bylongitudinal grooves 130 formed along the longitudinal axis L of implant100. In one embodiment, longitudinal grooves 130 have a V-shapedhorizontal cross-section. The lower most portions of left and right sidefacets 132, 134 of consecutive side-by-side projections 122 can becoincident with each other or may be spaced apart, any spacetherebetween can be at least in part flat, curved, sloped or otherwiseconfigured. Each surface projection 122 has left and right side facets132, 134 that converge to form a high point or peak 136 at the top ofeach surface projection 122. Each peak 136 can be aligned along linesthat are perpendicular, parallel, and/or diagonally oriented tolongitudinal axis L of implant 100. The left and right side facets 132,134 resist side-to-side motion of implant 100 after it is inserted intothe implantation space. Peaks 136 engage the bone of vertebral bodies Vadjacent to implant 100 in the implantation site. It is appreciated thatin a variation of the present invention, the peaks may be modified suchas to be truncated or cut off to have a broader rather than sharperupper most surface. Moreover, the peaks can be cleaved in one or moredirections so as to increase the surface area useful for engaging thebone of the vertebral bodies. The relieved areas of the cleavedprojections are useful for containing and carrying fusion promotingsubstances other than bone such as bone morphogenetic proteins andgenetic materials coding for the production of bone, or bone itselfwhich could by way of example be in the form of a paste. It is furtherappreciated that for all the various embodiments of the surfaceconfiguration of the present invention, longitudinal grooves 130 canhave horizontal cross-sections in a variety of configurations such as,without limitation, square-shaped or U-shaped configurations.

[0047] Sequential projections can be positioned on an implant whereineach surface projection has forward facing facets facing the samedirection such that consecutive projections are oriented forward facingfacet to rearward facing facet. The lower most portion of the slope ofthe forward facing facet of a first surface projection in a sequence canbe coincident with the rearward facet of the next surface projection inthe sequence. Alternatively, the forward facet of a first surfaceprojection and the rearward facet of the next surface projection in asequence can be spaced apart and the space can be at least in part flat,curved, or any other surface configuration suitable for the intendeduse. The surface projections can be oriented relative to one another toform an array and are preferably geometrically disposed relative to oneanother in a pattern wherein at least a portion of the projection isaligned along a longitudinal, horizontal, diagonal, or curved line.Further, it is appreciated that the surface of the present invention canbe useful with spinal implants of various configurations, includingconfigurations wherein at least one of leading end, trailing end, andsides of the spinal implant is curved. By way of example and notlimitation, the leading end, trailing end, and sides of the spinalimplant can form an oval, an oblong, or a circle. As shown in FIGS.8-11, a second embodiment of the surface configuration of the presentinvention is generally referred to by the numeral 220. Surfaceconfiguration 220 includes surface projections 222 to facilitateinsertion of implant 100 into an implantation site while resistingexpulsion of implant 100 in a direction opposite to the direction ofinsertion. Each of surface projections 222 has an angled forward facet224 directed at least in part toward leading end 202 of implant 100 anda rearward facet 226 directed at least in part toward trailing end 204of implant 100. Forward facet 224 has a length greater than the lengthof rearward facet 226. Rearward facet 226 has a slope that is steeperthan the slope of forward facet 224. In this embodiment, the base ofrearward facet 226 forms an angle of approximately 45 degrees withrespect to upper and/or lower surfaces 206, 208 of implant 100. Each oneof surface projections 222 has a left side facet 232 and a right sidefacet 234 directed toward the sides of implant 100, and forward facet224 and rearward facet 226.

[0048] In this embodiment of surface configuration 220, longitudinalgrooves 230 have a V-shaped horizontal cross-section. The lower mostportions of left and right side facets 232, 234 of consecutiveside-by-side projections 222 can be coincident with each other or may bespaced apart, any space therebetween can be at least in part flat,curved, sloped or otherwise configured. Each surface projection has leftand right side facets 232, 234 that converge to form a high point orpeak 236 at the top of each surface projections 222. Each peak 236 canbe aligned along lines that are perpendicular, parallel, and/ordiagonally oriented to the longitudinal axis L of implant 100. The leftand right side facets 232, 234 resist side-to-side motion of implant 100after it is inserted into the implantation space. Peaks 236 engage thebone of the vertebral bodies adjacent to implant 100 in the implantationsite.

[0049] As shown in FIGS. 12-15, a third embodiment of the surfaceconfiguration of the present invention is generally referred to by thenumeral 320 is shown. Surface configuration 320 includes surfaceprojections 322 to facilitate insertion of implant 100 into animplantation site while resisting expulsion of implant 100 in adirection opposite to the direction of insertion. Each of surfaceprojections 322 has an angled forward facet 324 directed at least inpart toward leading end 302 of implant 100 and a rearward facet 326directed at least in part toward trailing end 304 of implant 100.Forward facet 324 has a length greater than the length of rearward facet326. Rearward facet 326 has a slope that is steeper than the slope offorward facet 324. In this embodiment, the base of rearward facet 326 is“back cut” to form an angle greater than 90 degrees with respect toupper and/or lower surfaces 306, 308 of implant 100. The configurationof rearward facet 326 further enhances resistance of motion of theimplant in a direction opposite to the direction of insertion. It isappreciated that the angle of the base of rearward facet 326 withrespect to upper and/or lower surfaces 306, 308 of implant 100 can beany other angle suitable for the intended purpose of the presentinvention. Each one of surface projections 322 has a left side facet 332and a right side facet 334 directed toward the sides of implant 100, anda forward facet 324 and a rearward facet 326.

[0050] In this embodiment of surface configuration 320, longitudinalgrooves 330 have a V-shaped horizontal cross section. The lower mostportions of left and right side facets 332, 334 of consecutiveside-by-side projections 322 can be coincident with each other or may bespaced apart, and any space therebetween can be at least in part flat,curved, sloped or otherwise configured. Each surface projection 322 hasleft and right side facets 332, 334 that converge to form a high pointor peak 336 at the top of each surface projection 322. Each peak 336 canbe aligned along lines that are perpendicular, parallel, and/ordiagonally oriented to the longitudinal axis L of implant 100. The leftand right side facets 332, 334 resist side-to-side motion of implant 100after it is inserted into the implantation space. Peaks 336 engage thebone of vertebral bodies V adjacent to implant 100 in the implantationsite.

[0051] As shown in FIGS. 16-19B, a fourth embodiment of the surfaceconfiguration of the present invention is generally referred to by thenumeral 420. Surface configuration 420 includes surface projections 422configured to facilitate insertion of implant 100 in the direction ofinsertion into an implantation site while resisting expulsion of implant100 in a direction opposite to the direction of insertion. Each ofsurface projections 422 has an angled forward facet 424 directed towardleading end 402 of implant 100 and a rearward portion 426 directedtoward trailing end 404 of implant 100. Forward facet 424 has a lengthgreater than the length of rearward portion 426. Rearward portion 426has a slope that is steeper than the slope of forward facet 424. In thisembodiment, the base of rearward portion 426 forms an angle ofapproximately 90 degrees with respect to upper and/or lower surfaces406, 408 of implant 100. Rearward portion 426 can be a portion ofsurface projection 422, such as a facet, an edge, or a line for example.Each one of surface projections 422 has a left side forward facet 450, aright side forward facet 452, a left side rearward facet 454, and aright side rearward facet 456 directed toward the front and sides, anddirected toward the rear and sides of implant 100, respectively, andforward facet 424 and rearward portion 426.

[0052] Surface configuration 420 can further include a second pluralityof surface projections 460 having at least a left forward side facet 462and a right forward side facet 464 directed at least in part towardleading end 402 and sides of implant 100, respectively, and at least onerearward facet 466 directed at least in part toward trailing end 400.Left and right forward side facets 462, 464 have at least a firstportion in a plane at an angle to the longitudinal axis of implant 100.Second surface projections 460 can be interspersed with surfaceprojections 422.

[0053] Surface configuration 420 can further comprise a third pluralityof surface projections 470 having at least a left rearward side facet472 and a right rearward side facet 474 directed at least in part towardtrailing end 404 and sides of implant 100, respectively, and at leastone forward facet 476 directed at least in part toward leading end 402.Left and right rearward side facets 472, 474 have at least a firstportion in a plane at an angle to the longitudinal axis of implant 100.Third surface projections 470 can be interspersed with surfaceprojections 422 and/or second surface projections 460. Surfaceprojections 422 may have a length approximating the combined length ofsecond surface projections 460 and third surface projections 470.

[0054] In this embodiment, surface configuration 420 has angled grooves440 a-k that form a plurality of surface projections 422. In thisexample, angled grooves 440 a-k are formed at an angle that isapproximately 45 degrees to longitudinal axis L of spinal implant 100and in this example, angled grooves 440 a-k are approximately 90 degreesto one another. The angled grooves 440 a-k can be formed, if machined,by first passing a cutting element at a 45 degree angle to thelongitudinal axis L of implant 100 and then passing the cutting elementat a 90 degree angle to the path of the first pass of the cuttingelement, or otherwise formed by casting, molding, and other methods forforming a surface configuration. It is appreciated that angled grooves400 a-k can be formed at various angles to the longitudinal axis L ofimplant 100 and to each other. For example, such angles can be less than180 degrees.

[0055] In this embodiment of surface configuration 420, angled grooves440 a-k have a V-shaped horizontal cross-section. Each surfaceprojection 422 has left and right side facets 432 and 434 that areconvergent and form a high point or peak 436 at the top of each surfaceprojections 422. Each peak 436 can be aligned along lines that arehorizontally, longitudinally, and/or diagonally oriented along implant100. The left and right side forward and rearward facets 450, 452, 454,456 function to prevent side-to-side motion of implant 100 after it isinserted into the implantation space. Peaks 436 may also function liketeeth to engage the bone of vertebral bodies V adjacent to the implantin the implantation site.

[0056]FIG. 19B shows a variation of second and third surface projections460′, 470′ that can be cleaved in one or more directions to increase thenumber of exposed sides of each projection and thus increase the surfacearea of the implant bone engaging surface available to contact the boneof the vertebral bodies. A preferred embodiment of this variation of thesecond and third surface projections 460′, 470′ are cleaved by alongitudinal groove.

[0057] As shown in FIGS. 20-23, a fifth embodiment of the surfaceconfiguration of the present invention is generally referred to by thenumeral 520. Surface configuration 520 includes surface projections 522to facilitate insertion of implant 100 into an implantation site whileresisting expulsion of implant 100 in a direction opposite to thedirection of insertion. Surface projections 522 can be cleaved in one ormore directions to increase the number of exposed sides of eachprojection and thus increase the surface area of the implant boneengaging surface available to contact the bone of the vertebral bodies.For example, the surface projections can be cleaved by a longitudinalcut 540 generally parallel to the longitudinal axis L of implant 100 toform a surface projection having nine exposed sides. The surfaceprojections may further be cleaved by a horizontal cut 542 generallyperpendicular to the longitudinal axis L of implant 100 to form asurface projection having eighteen exposed sides. The cuts can penetratethe surface projection at a depth substantially equal to that of theheight of the surface projections as measured from the upper or lowersurfaces of the implant. The cuts can be oriented along at least one ofthe longitudinal axis of the implant, an axis perpendicular to thelongitudinal axis of said implant, and an axis at an angle between thelongitudinal axis and the axis perpendicular to the longitudinal axis ofthe implant. It is appreciated that cuts 540 and 542 may be formed aspart of the molding process for forming the surface projections.

[0058] When cleaved by longitudinal cut 540 and horizontal cut 542, eachof surface projections 522 has angled forward facet 524 a, 524 bdirected at least in part toward leading end 502 of implant 100 andrearward facets 526 a, 526 b directed at least in part toward trailingend 504 of implant 100. Forward facet 524 has a length greater than thelength of rearward facet 526. Rearward facets 526 a, 526 b have a slopethat is steeper than the slope of forward facets 524 a, 524 b. Thecleaved portion of surface projection 522 can be spaced apart by apredetermined distance and the space can be at least in part flat,curved, or any other surface configuration suitable for the intendeduse. In this embodiment, the base of rearward facets 526 a, 526 b formsan angle of approximately 45 degrees with respect to upper and/or lowersurfaces 506, 508 of implant 100. Each one of surface projections 522has left side facets 532 a, 532 b and right side facets 534 a, 534 bdirected toward the sides of implant 100, and forward facets 524 a, 524b and rearward facet 526 a, 526 b. In this embodiment of surfaceconfiguration 520, longitudinal grooves 530 have a V-shaped horizontalcross-section and each surface projection 522 has left and right sidefacets 532 a, 532 b, 534 a, 534 b that converge toward one another. Theleft and right side facets 532 a, 532 b, 534 a, 534 b resistside-to-side motion of implant 100 after it is inserted into theimplantation space. The surface configuration of the present inventioncan be formed by molding, machining or otherwise. A preferred surfaceconfiguration of the present invention may readily be machined bymilling from side to side, across the upper and lower vertebral bodyengaging surfaces, surface projections. A milling machine with a cuttingtool having an angled cutting face such as a V-shaped profile can thenbe run through the plurality of surface projections parallel to thelongitudinal axis of the implant to form the above-described surface. Ina preferred embodiment, the V-shaped cutting tool of the milling machinehas faces with an angle of approximately 90 degrees, which faces are ata 45-degree angle to the plane of the surfaces being so machined.Without departing from the present invention, the angle of the cuttingfaces can be more or less than 90 degrees, the angle of the cutting faceto the surface to be cut can be more or less than 45 degrees, and ratherthan running the cutter element parallel to the longitudinal axis of theimplant, the cutting element may be run at an angle. By way of exampleonly and not limitation, this angle may be at 45 degrees to thelongitudinal axis of the implant and each surface projection can beformed by two grooves crossing the projections at a 90 degree angle toeach other.

[0059] The spinal implants of the present invention are made ofartificial or naturally occurring materials suitable for implantation inthe human spine. The implants can comprise bone including, but notlimited to, cortical bone, materials other than bone, such as metalsincluding, but not limited to, titanium and its alloys or ASTM material,surgical grade plastics, plastic composites, ceramics, or othermaterials suitable for use as a spinal implant. The implants of thepresent invention can further comprise or be combined with bone growthpromoting materials, including but not limited to, bone, bonemorphogenetic proteins, hydroxyapatite, and genes coding for theproduction of bone. The implants can be treated with a bone growthpromoting substance, can be a source of osteogenesis, or can bebioabsorbable at least in part. The implants of the present inventioncan be formed of a porous material.

[0060] The spinal implants of the present invention can be for thepurpose of achieving fusion. The upper and lower surfaces of the fusionimplants can include at least one opening, each in communication withthe other, to permit for the growth of bone from vertebral body toadjacent vertebral body through the implant. The implant can have aninternal chamber and may also have an access opening for accessing theinternal chamber, in which case the implant can further have a coversuch as a cap 101′ (shown in FIG. 1A) to close the access opening atleast in part. Openings in the upper and lower surfaces of the implantcan communicate with the internal chamber to permit further growth ofbone from vertebral body to adjacent vertebral body through the implant.The internal chamber can contain bone growth promoting materials,including but not limited to, bone, bone morphogenetic proteins,hydroxyapatite, and genes coding for the production of bone. Theimplants of the present invention can be formed of a material thatintrinsically participates in the growth of bone from one of theadjacent vertebral bodies to the other of the adjacent vertebral bodies.

[0061] While various embodiments of the present invention are presentedby way of example only and not limitation, common to each of them, isthat the configuration of the surface is based on a plurality of surfaceprojections disposed in arrays, each surface projection comprising atleast one leading facet and at least one opposing trailing facet, inwhich the leading facet has a length greater than the trailing facet andthe trailing facet has a steeper slope than the slope of the leadingfacet. The surface configuration is located on at least a portion of oneof the opposed vertebral body engaging surfaces of the spinal implant.

[0062] While the implant shown in FIGS. 1, 2, and 3 is an interbodyspinal fusion implant, it is appreciated that the surface configurationof the present invention is applicable to any interbody spinal fusionimplants, including but not limited to, an artificial disc or motionpreserving device having opposed surfaces incorporating the presentinventive teachings for engaging each of the adjacent vertebral bodies.

[0063] It is believed that the operation and construction of the presentinvention will be apparent from the foregoing description and, while theinvention shown and described herein has been characterized asparticular embodiments, changes and modifications may be made thereinwithout departing from the spirit and scope of the invention as definedin the following claims.

What is claimed is:
 1. An interbody spinal implant for insertion betweenadjacent vertebral bodies of a human spine, said implant comprising: aleading end for introduction of said spinal implant into the spine, anopposite trailing end, spaced apart sides therebetween, and amid-longitudinal axis passing through said leading and trailing ends;opposite upper and lower surfaces between said leading and trailing endsand said spaced apart sides, said upper surface adapted for placement inengagement with the bone of one of the vertebral bodies and saidopposite lower surface adapted for placement in engagement with the boneof the other of the vertebral bodies when said implant is placed betweenthe adjacent vertebral bodies; and a plurality of surface projectionsformed on said upper and lower surfaces of said implant, each of saidsurface projections having a plurality of facets, each of said facetshaving a perimeter defining each facet, at least a first and a second ofsaid surface projections each having at least one facet with theperimeter having at least a first and a second portion arranged to forman included angle greater than 90 degrees between said first and secondportions.
 2. The spinal implant of claim 1, wherein one of said facetsis formed in the shape of a triangle having a vertex with an includedangle greater than 90 degrees.
 3. The spinal implant of claim 1, whereineach of said forward facet and said rearward facet of said first andsecond projections have a length and a slope, the length of said forwardfacet being longer than the length of said rearward facet, the slope ofsaid rearward facet being steeper than the slope of said forward facet.4. The spinal implant of claim 1, wherein said rearward facet is at anangle to at least one of said upper and lower surfaces of said implant.5. The spinal implant of claim 4, wherein said angle is greater than 90degrees.
 6. The spinal implant of claim 1, wherein said surfaceprojections are oriented relative to one another to form an array. 7.The spinal implant of claim 1, wherein said surface projections aregeometrically disposed relative to one another.
 8. The spinal implant ofclaim 1, wherein said upper and lower surfaces of said implant are atleast in part arcuate.
 9. The spinal implant of claim 1, wherein atleast one of said leading end, trailing end, and sides are curved. 10.The spinal implant of claim 1, wherein said sides are curved.
 11. Thespinal implant of claim 1, wherein each of said leading end, trailingend, and sides are curved.
 12. The spinal implant of claim 11, whereinsaid leading end, trailing end, and sides form a circle.
 13. The spinalimplant of claim 1, wherein said upper and lower surfaces of saidimplant are at least in part planar.
 14. The spinal implant of claim 1,wherein said upper and lower surfaces converge toward each other alongat least a portion of the length of said implant.
 15. The spinal implantof claim 1, wherein said implant comprises a material other than bone.16. The spinal implant of claim 1, wherein said implant comprises bone.17. The spinal implant of claim 16, wherein said bone includes corticalbone.
 18. The spinal implant of claim 1, wherein said implant comprisesbone growth promoting material.
 19. The spinal implant of claim 18,wherein said bone growth promoting material is one of bone morphogeneticprotein, hydroxyapatite, and genes coding for the production of bone.20. The spinal implant of claim 1, wherein said implant is treated witha bone growth promoting substance.
 21. The spinal implant of claim 1,wherein said implant is a source of osteogenesis.
 22. The spinal implantof claim 1, wherein said implant is at least in part bioabsorbable. 23.The spinal implant of claim 1, wherein said implant comprises metal. 24.The spinal implant of claim 23, wherein said metal is ASTM materialsuitable for use as a spinal fusion implant.
 25. The spinal implant ofclaim 23, wherein said metal includes titanium.
 26. The spinal implantof claim 1, wherein said implant comprises a plastic material.
 27. Thespinal implant of claim 1, wherein said implant comprises a ceramicmaterial.
 28. The spinal implant of claim 1, wherein said implant isformed of a porous material.
 29. The spinal implant of claim 1, whereinsaid implant is formed of a material that intrinsically participates inthe growth of bone from one of the adjacent vertebral bodies to theother of the adjacent vertebral bodies.
 30. The spinal implant of claim1, wherein said implant is a motion preserving device adapted to spaceapart and allow motion between the adjacent vertebral bodies.
 31. Thespinal implant of claim 1, wherein said spinal implant is a fusionimplant.
 32. The spinal implant of claim 31, wherein said upper andlower surfaces include at least one opening to permit bone growth fromadjacent vertebral body to adjacent vertebral body through said implant.33. The spinal implant of claim 31, wherein said implant has an internalchamber and an access opening for accessing said internal chamber. 34.The spinal implant of claim 33, wherein said implant has a cap forclosing said access opening.
 35. The spinal implant of claim 33, whereinsaid upper and lower surfaces include at least one opening incommunication with said internal chamber to permit bone growth fromadjacent vertebral body to adjacent vertebral body through said implant.36. The spinal implant of claim 33, wherein said internal chamber iscapable of containing bone growth promoting material.
 37. The spinalimplant of claim 36, wherein said bone growth promoting material is oneof bone morphogenetic protein, hydroxyapatite, and genes coding for theproduction of bone.
 38. The spinal implant of claim 1, furthercomprising at least one opening capable of retaining fusion promotingmaterials.
 39. The spinal implant of claim 1, in combination with afusion promoting substance.
 40. The spinal implant of claim 39, whereinsaid fusion promoting substance includes at least one of bone, bonemorphogenetic protein, hydroxyapatite, and genes coding for theproduction of bone.
 41. The spinal implant of claim 1, wherein each ofsaid first and second surface projections have a base, said bases beingadjacent to one another.
 42. The spinal implant of claim 1, wherein eachof said first and second surface projections have a base, said basesbeing spaced apart from one another along a direction generally parallelto the mid-longitudinal axis of said implant.
 43. The spinal implant ofclaim 1, wherein each of said first and second surface projections havea base, said bases being spaced apart from one another along a directiongenerally transverse to the mid-longitudinal axis of said implant. 44.The spinal implant of claim 1, wherein said forward facets of each ofsaid first and second surface projections face the same direction. 45.The spinal implant of claim 1, wherein said first and second surfaceprojections each have opposed side facets directed generally toward saidspaced apart sides of said implant, respectively, said side facets beinglocated between said forward facet and said rearward facet of each ofsaid first and second surface projections, said side facets convergingtoward each other in a direction away from one of said upper and lowersurfaces of said implant.
 46. The spinal implant of claim 45, whereinsaid opposed side facets intersect each other.
 47. The spinal implant ofclaim 46, wherein said opposed side facets converge to form a peak atthe top of said surface projection.
 48. The spinal implant of claim 47,wherein said peaks of at least two of said surface projections arealigned along lines that are at least one of perpendicular, parallel,and diagonal to the mid-longitudinal axis of said implant.
 49. Thespinal implant of claim 47, wherein said peak of said first surfaceprojection overlies at least a portion of said second surfaceprojection.
 50. The spinal implant of claim 47, wherein said peaks ofsaid first and second surface projections are at the same height aboveone of said upper and lower surfaces of said implant.
 51. The spinalimplant of claim 45, wherein adjacent side facets of adjacent surfaceprojections are spaced apart to define a groove therebetween.
 52. Thespinal implant of claim 45, wherein a plurality of adjacent surfaceprojections are spaced apart to form a plurality of groovestherebetween.
 53. The spinal implant of claim 52, wherein at least oneof said grooves is parallel to the mid-longitudinal axis of saidimplant.
 54. The spinal implant of claim 52, wherein at least two ofsaid grooves cross each other.
 55. The spinal implant of claim 52,wherein at least one of said grooves has a horizontal cross-sectionalshape that is one of a v-shape, u-shape, and a box-like shape.
 56. Thespinal implant of claim 45, wherein each of said first and secondsurface projections have a base and said side facets have a maximumwidth therebetween at said base, said base being spaced apart from abase of another of said surface projections by a distance no greaterthan one-half the maximum width of one of said first and second surfaceprojections.
 57. An interbody spinal implant for insertion betweenadjacent vertebral bodies of a human spine, said implant comprising: aleading end for introduction of said spinal implant into the spine, anopposite trailing end, spaced apart sides therebetween, and amid-longitudinal axis passing through said leading and trailing ends;opposite upper and lower surfaces between said leading and trailing endsand said spaced apart sides, said upper surface adapted for placement inengagement with the bone of one of the vertebral bodies and saidopposite lower surface adapted for placement in engagement with the boneof the other of the vertebral bodies when said implant is placed betweenthe adjacent vertebral bodies; and a plurality of surface projectionsformed on said upper and lower surfaces of said implant, at least afirst and a second of said surface projections each having at least oneforward facing facet directed at least in part toward said leading endand at least one rearward facet directed at least in part toward saidtrailing end, each of said forward facet and rearward facet having alength and a slope, the length of said forward facet being longer thanthe length of said rearward facet, the slope of said rearward facetbeing steeper than the slope of said forward facet, said first andsecond surface projections each forming a base and a portion above saidbase, said portion above the base of said first and second surfaceprojections extending outside of the perimeter of the base of arespective one of said first and second surface projections.
 58. Thespinal implant of claim 57, wherein said rearward facet is at an angleto at least one of said upper and lower surfaces of said implant. 59.The spinal implant of claim 58, wherein said angle is greater than 90degrees.
 60. The spinal implant of claim 57, wherein said surfaceprojections are oriented relative to one another to form an array. 61.The spinal implant of claim 57, wherein said surface projections aregeometrically disposed relative to one another.
 62. The spinal implantof claim 57, wherein said upper and lower surfaces of said implant areat least in part arcuate.
 63. The spinal implant of claim 57, wherein atleast one of said leading end, trailing end, and sides are curved. 64.The spinal implant of claim 57, wherein said sides are curved.
 65. Thespinal implant of claim 57, wherein each of said leading end, trailingend, and sides are curved.
 66. The spinal implant of claim 65, whereinsaid leading end, trailing end, and sides form a circle.
 67. The spinalimplant of claim 57, wherein said upper and lower surfaces of saidimplant are at least in part planar.
 68. The spinal implant of claim 57,wherein said upper and lower surfaces converge toward each other alongat least a portion of the length of said implant.
 69. The spinal implantof claim 57, wherein said implant comprises a material other than bone.70. The spinal implant of claim 57, wherein said implant comprises bone.71. The spinal implant of claim 70, wherein said bone includes corticalbone.
 72. The spinal implant of claim 57, wherein said implant comprisesbone growth promoting material.
 73. The spinal implant of claim 72,wherein said bone growth promoting material is one of bone morphogeneticprotein, hydroxyapatite, and genes coding for the production of bone.74. The spinal implant of claim 57, wherein said implant is treated witha bone growth promoting substance.
 75. The spinal implant of claim 57,wherein said implant is a source of osteogenesis.
 76. The spinal implantof claim 57, wherein said implant is at least in part bioabsorbable. 77.The spinal implant of claim 57, wherein said implant comprises metal.78. The spinal implant of claim 77, wherein said metal is ASTM materialsuitable for use as a spinal fusion implant.
 79. The spinal implant ofclaim 77, wherein said metal includes titanium.
 80. The spinal implantof claim 57, wherein said implant comprises a plastic material.
 81. Thespinal implant of claim 57, wherein said implant comprises a ceramicmaterial.
 82. The spinal implant of claim 57, wherein said implant isformed of a porous material.
 83. The spinal implant of claim 57, whereinsaid implant is formed of a material that intrinsically participates inthe growth of bone from one of the adjacent vertebral bodies to theother of the adjacent vertebral bodies.
 84. The spinal implant of claim57, wherein said implant is a motion preserving device adapted to spaceapart and allow motion between the adjacent vertebral bodies.
 85. Thespinal implant of claim 57, wherein said spinal implant is a fusionimplant.
 86. The spinal implant of claim 85, wherein said upper andlower surfaces include at least one opening to permit bone growth fromadjacent vertebral body to adjacent vertebral body through said implant.87. The spinal implant of claim 85, wherein said implant has an internalchamber and an access opening for accessing said internal chamber. 88.The spinal implant of claim 87, wherein said implant has a cap forclosing said access opening.
 89. The spinal implant of claim 87, whereinsaid upper and lower surfaces include at least one opening incommunication with said internal chamber to permit bone growth fromadjacent vertebral body to adjacent vertebral body through said implant.90. The spinal implant of claim 87, wherein said internal chamber iscapable of containing bone growth promoting material.
 91. The spinalimplant of claim 90, wherein said bone growth promoting material is oneof bone morphogenetic protein, hydroxyapatite, and genes coding for theproduction of bone.
 92. The spinal implant of claim 57, furthercomprising at least one opening capable of retaining fusion promotingmaterials.
 93. The spinal implant of claim 57, in combination with afusion promoting substance.
 94. The spinal implant of claim 93, whereinsaid fusion promoting substance includes at least one of bone, bonemorphogenetic protein, hydroxyapatite, and genes coding for theproduction of bone.
 95. The spinal implant of claim 57, wherein each ofsaid first and second surface projections have a base, said bases beingadjacent to one another.
 96. The spinal implant of claim 57, whereineach of said first and second surface projections have a base, saidbases being spaced apart from one another along a direction generallyparallel to the mid-longitudinal axis of said implant.
 97. The spinalimplant of claim 57, wherein each of said first and second surfaceprojections have a base, said bases being spaced apart from one anotheralong a direction generally transverse to the mid-longitudinal axis ofsaid implant.
 98. The spinal implant of claim 57, wherein said forwardfacets of each of said first and second surface projections face thesame direction.
 99. The spinal implant of claim 57, wherein said firstand second surface projections each have opposed side facets directedgenerally toward said spaced apart sides of said implant, respectively,said side facets being located between said forward facet and saidrearward facet of each of said first and second surface projections,said side facets converging toward each other in a direction away fromone of said upper and lower surfaces of said implant.
 100. The spinalimplant of claim 99, wherein said opposed side facets intersect eachother.
 101. The spinal implant of claim 100, wherein said opposed sidefacets converge to form a peak at the top of said surface projection.102. The spinal implant of claim 101, wherein said peaks of at least twoof said surface projections are aligned along lines that are at leastone of perpendicular, parallel, and diagonal to the mid-longitudinalaxis of said implant.
 103. The spinal implant of claim 101, wherein saidpeak of said first surface projection overlies at least a portion ofsaid second surface projection.
 104. The spinal implant of claim 101,wherein said peaks of said first and second surface projections are atthe same height above one of said upper and lower surfaces of saidimplant.
 105. The spinal implant of claim 99, wherein adjacent sidefacets of adjacent surface projections are spaced apart to define agroove therebetween.
 106. The spinal implant of claim 99, wherein aplurality of adjacent surface projections are spaced apart to form aplurality of grooves therebetween.
 107. The spinal implant of claim 106,wherein at least one of said grooves is parallel to the mid-longitudinalaxis of said implant.
 108. The spinal implant of claim 106, wherein atleast two of said grooves cross each other.
 109. The spinal implant ofclaim 106, wherein at least one of said grooves has a horizontalcross-sectional shape that is one of a v-shape, u-shape, and a box-likeshape.
 110. The spinal implant of claim 99, wherein each of said firstand second surface projections have a base and said side facets have amaximum width therebetween at said base, said base being spaced apartfrom a base of another of said surface projections by a distance nogreater than one-half the maximum width of one of said first and secondsurface projections.